Clasps and Levers Flashcards
three components of a clasp assembly
- rest
- retainer (retention)
- bracer
Type I clasp aka
suprabulge (above height of contour)
Type II clasp aka
infrabulge
Describe type I clasp
- origin
- retention
Occlusal in origin and FROM MINOR CONNECTOR
CROSSES BULGE (height of contour) and is ONLY RETENTIVE IN THE TERMINAL 1/3
retention can be on either the buccal or the lingual but NEVER BOTH
- so only one undercut per tooth
examples of type I clasps
- circumferential - “C” clasp
- combination - combo
- ring
- embrasure
retention and material for C (akers) clasp
Retention may be buccal OR lingual
Retention may be mesial OR distal
Material may be cast or wrought
- may be on framework or soldered on
material for C clasp
Casting = tapered
- stronger and thick and ONE-PIECE CASTING
Wrought wire = round
- wire arm soldered or welded to frame work
what do wrought wire clasps require?
requires soldering or welding which requires access to an open proximal surface
- bulky solder joints
wire claps cannot originate from where?
Embrassures
T/F Combo clasps can be used in areas with large cervical convergences and undercuts?
TRUE
- clasp we would use here
material to make combo clasp?
Cast and wrought wire
- it is a C with a WIRE RETENTIVE ARM
- must be soldered or welded to casting
origin of combo clasp
EDENTULOUS space
flexibility of combo clasp
3 times MORE flexible than cast claps
which is more subject to breakage, combo or cast clasp?
Combo
protection in combo clasp?
Protects tooth AT ITS OWN EXPENSE
Use of a ring clasp?
used on lone -standing MOLARS
used ONLY in non-rotating partials
characteristics of a ring clasp
- 2 rests
- 2 minor connectors
- has almost continous contact on the tooth
- helps INCREASE BRACING – continuous bracing arm
what are disadvantages to embrasure clasps?
- lack guide planes
- places clasps too close together
- may act as an interproximal wedge
- may cause occlusal or esthetic problems
what determines a clasp flexibility
- material
- length
- thickness
- straightness
- cross-sectional shape
clasp flexibility: material
Cr-Co < Au (gold) < wire
- wire is most flexible
clasp flexibility: length
short < long
short is less flexible
6mm minimum
clasp flexibility: thickness
tip should taper
clasp flexibility: staightness
bends decrease flexibility
should contain less bends as possible
clasp flexibility: cross - sectional shape
flat < round
flat is less flexible than round
shape of cast clasp
1/2 round
COMBO = wrought - ROUND
what should the tip of a clasp always be?
tapered and should be trimmed and polished to shape after casting
*not paddle shaped
origin and finish of type 1 clasp
occlusal in origin –> from minor connector–>crossed bulge –. and retentive last 1/3 of it ends in the undercut
retention can be on the buccal or lingual aspect
in type 1 clasp retention arm called retention arm but in type II what are they called?
APPROACH arm (vertical)
Retainer (horizontal)
origin of type II clasp
gingival
where does type II clasp come from
gingival and FROM MESHWORK (not minor connector like type 1 clasp)
type II clasp location in reference to the bulge
stays below the bulge
- so all of it is considered retentive
where is the retention on a type II clasp?
ALWAYS ON THE BUCCAL
Examples of type II clasps
- Bar
- T- bar
- RPI
when you have an approach arm that means you must have what?
an approach arm
describe a bar (roach or J bar) clasp
this is a type 2 clasp
retention : DISTO-BUCCAL ONLY
which contacts less tooth surface? C clasp or Bar?
Bar
when is bar contraindicated
when an approach arm is contraindicated
T- bar clasp description
major difference is that the mesial aspect of the retentive part is above the survey line meaning it is NOT RETENTIVE BUT BRACING
- utilized when we do not have enough bracing on the opposite side of the tooth
*retention is still DB only
what does RPI stand for? what type of clasp?
R- Rest
P -Proximal plate
I - bar
type II clasp
RPI metal touching teeth?
less than a T and less than a bar clasp
retention on RPI
mid or mesial buccal only
rest in RPI for pre-molars?
for cuspids?
pre-molars on mesio-occlusal
on cuspids = on mesio-lingual
bracing for RPI
2 minor connectors only and has least amount of metal when compared to any other clasp
minimum distance for any type 2 clasp?
2 mm from the free gingival margin for any undercut
3mm in height before it starts to swing back and join the framework
orientation of the approach arm to the free gingival margin in an RPI?
the approach arm is perpendicular to the free gingival margin
where you can use approach arms?
Can:
tooth = tissue (ideally) (.01 undercut) and tissue is 3mm below)
TISSUE UNDERCUT below 3mm - so goes into undercut after you alwready have the 3mm you need
ledge - okay again if you have 3mm and then it ledges out (we can contour the approach arm to the ledge)
where/ when are approach arms contra-indicated?
- tissue undercut above 3mm (do not have the 3mm distance we need) tissue immediately goes into undercut
- SEVERE TILT - if we try to adjust tooth - prepping too much
- way too much space between arm and tooth
implication of a space between tissue and approach arm?
it will become a food trap and cause lip irritation
amount of tissue that needs to be surveyed for a type II clasp?
3 mm
how to reduce a tissue ndercut?
tail down A/P tilt or laterally tilting it away
enamoloplasty
five incorrect uses for aproach arms?
- double arms
- skipping of teeth
- lingual or palatal
- reverse or distal (not going to swing an approach arm from an anterior tooth back)
- molars (for same reasons) – buccal shelf and zygomatic arch are there
* these are saying you do NOT USE THEM HERE
why would approach arm be contraindicated in molars?
because of location of buccal shelf and zygomatic arch
bracing aka
reciprocal
if she says ‘what is reciprocal’ she means what?
what is bracing
effect of pushing a fixed object
it will TIP unless something opposes it
three types of bracers
- bracing ARMS
- bracing BLANKETS (CONGULUM REST)
- bracing MINOR CONNECTORS
cingulum rest can also be referred to as what
blanket
advantage of using 2 minor connectors with a type 2 clasp?
least amount of metal touches the teeth from the lingual aspect
if there is a C clasp of canine/ cuspid what is the bracer?
Lingual BLANKET – but ONLY IN A NON-ROTATING PARTIAL
when do you use an arm for bracing and where
Molar or pre-molar only on buccal or lingual
when do you use 2 minor connectors and where
lingual of pre-molar or cuspid ONLY for type two claps
why can you not use 2 minor connectors on molars?
molars are TOO WIDE to be braced by 2 minor connectors
what type of bracing is used on canines of non-rotating partials?
BLANKET
major purpose of bracer
neutralize the effect of the retentive tip (so opposite of the retention aspect of clasp)
location of a bracer
must be MORE THAN 180 degrees from retentive tip
**directly opposite from the retainer
must be viewed from the OCCLUSAL and PROXIMAL
- At or slightly above the survey line because the retainer is below the survery line (hence the retention component of retainer)
Occlusal forces come from what?
rests
Lateral forces come from what?
clasps
clasps are placed where? why?
placed as gingivally as possible to reduce rotational or tipping forces
how do you lower survey line?
disk non-parallel to the path
two types of retentive undercuts
- bilateral
2. diametric opposition
bilateral opposition undercut location
all undercuts are on buccal or all undercuts are on the lingual
diametric opposition
there are undercuts on the lingual and on the buccal within same arch (maxilla or mandible)
ideal location of ubndercuts
all (bilateral opposition) on the buccal aspect so all stress on the framework is directed outwards
if all undercuts on lingual implication?
the stress on the frame is all directed inwards
if have B + L mix of undercuts?
stress on framework is directed sideways
mandibular molars typically tilt which way?
lingually
implication of a longer edentoulous space?
greater the potential of a lever action on the abutment teeth
definition of class I lever
the FULCRUM is placed BETWEEN the effort and the load
most common lever configuration
movement of load in effort in a class I lever
the movement of the load is in the OPPOSITE direction of the movement of the effort
Class 2 lever defintion
has the LOAD BETWEEN the effort and the fulcrum
movement of load and effort in class 2 lever
the movement of the load is in the SAME DIRECTION as that of the effort
location of fulcrum determines what
the lever
during rotation clasps act as?
Levers
the rest determines what for levers?
the CLASS of lever
implication of a longer lever arm?
more torque on abutment tooth – easier to dislodge (not good)
rest seat on the distal? implication in terms of levers?
1st class
rest seat on the mesial? implication in terms of levers?
2nd class lever
fulcrum is?
the rest
effort is the?
biting
resistance is the?
tooth
clasp tip movement in a 2nd class lever?
down and away from effort (biting)
clasp tip movement in a 1st class lever? implication?
up
- bite down and clasp tip moves up into the undercut
CAN EXTRACT TEETH
a rest closest to the rotation is what type lever?
class 1 lever
rest away from the axis of rotation is what type of lever?
class 2 lever
if have two rests on the teeth what class lever?
THE REST CLOSEST TO THE ROTATION = THE LEVER
you classify lever based on which one is closest to the axis of rotation so could still be class I
Rest on cuspid in a rotating partial?
MESIAL LINGUAL
cingulum/ blanket would include distal and would create a class 1 lever which we do not want
movement of a non- rotating partial?
up and down
do NOT act as levers
movement of a rotating partial?
move anterio-posterior
act as levers
ideal design for RPI clasp
short occlusal rest, short distal guide plane (occlusal 1/3) and mesial shifted I bar
biting force
36 psi
non rotating partials look like?
all edentulous spaces have TEETH AT EITHER END
all rotating partials have?
at least one edentulous space has soft tissue (no teeth) at one end
AKA distal extension
in non rotating partials describe what happens to the clasp in terms of active or passive?
when in place - passive
when lifted out of place = active (crosses survey line)
then becomes passive as it is past above survey line
then goes active to seat again
then once seated = becomes passive again
first and second choice of clasp for non-rotating partials?
- C clasp (simplest design)
2. any - b/c all non rotating alike
what happens if clasp tip is mesial to the rest?
the lever changes to a class I
so dont go past the mesial line angle
on cuspids and pre molars always stay mid buccal or just slightly mesial to this
only way an RPA can protect a tooth?
if used with a class 2 lever
order of clasp choice in rotating partial?
- RPI
- RPA COMBO
- Bar w/ 2nd class lever
- RPA cast
cast contact vs wire contact
cast –> surface contact
wire –> point contact
if teeth are week how do you design?
treat as a DE with RPI
if bone is week how do you treat?
treat as DE with combo
implication of having a lingual bracing arm with class i lever
when lift up the arm will torque the tooth because it goes into survey line
if use two minor connectors for bracing how does this help?
now there are two minor connectors and they rotate around the tooth
bite down – rest goes up and other slips into the gingival 1/3
lift up – guide plane and rest engage then other part will slide up
no metal on the lingual portion of the tooth
RPA combo location of rest and tip
MO rest
MB tip
RPI rest and tip location
MO rest
Mid B tip
Bar rest and tip location
MO rest
DB tip
RPA c rest and tip location
MO rest
MB tip
